Two important contexts to this review.
First, this is only for the Cravings breakfast, and the Cravings brunch (had both). I make no claims to the dinner service.
Second, my evaluation is done from a perspective that I am evaluating a buffet. I don't compare and rate a buffet with fine dining restaurants.
The Mirage breakfast buffet was acceptable, but it would not have been at full price (we were comp'd both times). The food is typical buffet quality. Not outstanding and not original. The options during the breakfast are surprisingly limited. This is even true at the omelet station where there are a limited number of ingredients. I walked away full, but felt those who paid full price would have been disappointed.
The brunch has many more options and comes with alcohol, however the price is significantly higher (again, I didn't pay it).
I'd have a hard time justifying the $20 price for the regular breakfast. If one has transportation, Sunset Station would offer a better buffet at less than half the price.
If you're on the strip and going to pay full price, I think you'd do much better at Cosmo (Wicked Spoon) or Aria.
The one place I felt the buffet might have had a slight edge was in the desserts. Some very good options there.
If you're comp'd, it's a fine. If you've got a two-for-one and you're already there, it's okay. If you're paying full price, go elsewhere.